Reality: How does consciousness fit in?

DESCARTES might have been onto something with “I think therefore I am”, but surely “I think therefore you are” is going a bit far? Not for some of the brightest minds of 20th-century physics as they wrestled mightily with the strange implications of the quantum world.

According to prevailing wisdom, a quantum particle such as an electron or photon can only be properly described as a mathematical entity known as a wave function. Wave functions can exist as “superpositions” of many states at once. A photon, for instance, can circulate in two different directions around an optical fibre; or an electron can simultaneously spin clockwise and anticlockwise or be in two positions at once.

When any attempt is made to observe these simultaneous existences, however, something odd happens: we see only one. How do many possibilities become one physical reality?

This is the central question in quantum mechanics, and has spawned a plethora of proposals, or interpretations. The most popular is the Copenhagen interpretation, which says nothing is real until it is observed, or measured. Observing a wave function causes the superposition to collapse.

However, Copenhagen says nothing about what exactly constitutes an observation. John von Neumann broke this silence and suggested that observation is the action of a conscious mind. It’s an idea also put forward by Max Planck, the founder of quantum theory, who said in 1931, “I regard consciousness as fundamental. I regard matter as derivative from consciousness.”

That argument relies on the view that there is something special about consciousness, especially human consciousness. Von Neumann argued that everything in the universe that is subject to the laws of quantum physics creates one vast quantum superposition. But the conscious mind is somehow different. It is thus able to select out one of the quantum possibilities on offer, making it real – to that mind, at least.

Henry Stapp of the Lawrence Berkeley National Laboratory in California is one of the few physicists that still subscribe to this notion: we are “participating observers” whose minds cause the collapse of superpositions, he says. Before human consciousness appeared, there existed a multiverse of potential universes, Stapp says. The emergence of a conscious mind in one of these potential universes, ours, gives it a special status: reality.

There are many objectors. One problem is that many of the phenomena involved are poorly understood. “There’s a big question in philosophy about whether consciousness actually exists,” says Matthew Donald, a philosopher of physics at the University of Cambridge. “When you add on quantum mechanics it all gets a bit confused.”

Donald prefers an interpretation that is arguably even more bizarre: “many minds”. This idea – related to the “many worlds” interpretation of quantum theory, which has each outcome of a quantum decision happen in a different universe – argues that an individual observing a quantum system sees all the many states, but each in a different mind. These minds all arise from the physical substance of the brain, and share a past and a future, but cannot communicate with each other about the present.

Though it sounds hard to swallow, this and other approaches to understanding the role of the mind in our perception of reality are all worthy of attention, Donald reckons. “I take them very seriously,” he says.

Michael Brooks is a consultant for New Scientist, and author of The Secret Anarchy of Science (Profile/Overlook)